Method and apparatus for irradiating laser

ABSTRACT

A laser irradiation process includes: scanning a substrate with laser having a predetermined lasing frequency at different irradiation intensities to form a plurality of first irradiation areas corresponding to the irradiation intensities; illuminating the first irradiation areas to reflected light receive from the first irradiation areas; determining microcrystallization intensity based on the received reflected light; and determining irradiation intensity based on the thus determined microcrystallization intensity. The laser irradiation process uses the irradiation intensity for irradiating a polycrystalline film in a product semiconductor device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of application Ser. No.11/737,640, filed Apr. 19, 2007.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2006-115710, filed on Apr. 19, 2006, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for irradiatinglaser and, more particularly, to the technique such as used in a laserannealing process performed for forming a polycrystalline thin film byirradiating a semiconductor thin film with a laser.

2. Description of the Related Art

A polycrystalline silicon thin film (referred to as polycrystalline-Sifilm hereinafter) is adopted as a conductive film of athin-film-transistor (TFT) device formed on a glass substrate, becauseof the easiness for processing. Generally, an excimer laser annealing(ELA) technique is employed to form the polycrystalline-Si film. In theELA process, an amorphous silicon thin film (referred to as amorphous-Sifilm hereianafter) is formed on the substrate, and a pulse beam ofexcimer laser is irradiated on the thus formed amorphous-Si film. Theamorphous-Si film is melted by the irradiation of the laser, and thenrecrystallized through a cooling down, consequently to form apolycrystalline-Si film. It is generally known that a larger grain sizeof the polycrystalline-Si film provides excellent properties for the TFTdevice, especially in the carrier mobility thereof. Therefore, it isdesired to form the crystal grain as large as possible in thepolycrystallization of the amorphous-Si film.

In the process of polycrystallizing the amorphous-Si film, along with anincrease in the irradiation intensity of laser, a shift is caused from acrystallization (ordinary crystallization) wherein a relatively largecrystal grain is obtained toward a microcrystallization wherein a finercrystal grain is obtained. The ordinary crystallization is caused whenthe amorphous-Si film is not completely melted, and thus nuclei aregenerated at random at the boundary surface between the solid phase andthe liquid phase of silicon or the boundary surface between theamorphous-Si film and the substrate, during the recrystallization. Inthe ordinary crystallization, the diameter of the crystal grainincreases as the irradiation intensity is increased.

On the other hand, the microcrystallization is caused when theamorphous-Si film is completely melted, and thus nuclei are generated ina relatively uniform state in the entire film, during therecrystallization. The diameter of the crystal grain created in themicrocrystallization is as small as 100 nm or below. In themicrocrystallization, the diameter of the crystal grain scarcely dependson the irradiation intensity. The threshold intensity of the laser atwhich the shift from the ordinary crystallization toward themicrocrystallization occurs is referred to as “microcrystallizationintensity”. The microcrystallization intensity is a parameter normalizedby the thickness of the amorphous-Si film in general.

As described above, in the process of polycrystallizing the amorphous-Sifilm, the shift from the ordinary crystallization toward themicrocrystallization, bounded by the microcrystallization intensity, isabruptly caused with an increase in the irradiation intensity of thelaser. That is, when the irradiation intensity of the laser exceeds themicrocrystallization intensity, the grain size of the resultantpolycrystalline-Si film extremely reduces, whereby a suitable grain sizeis not achieved. Therefore, in the process of polycrystallizing theamorphous-Si film, it is important to accurately determine themicrocrystallization intensity and set the irradiation intensity of thelaser smaller than the microcrystallization intensity.

Patent Publications JP-2000-114174A and JP-2002-8976A describe atechnique for determining the microcrystallization intensity. Accordingto these patent publications, prior to actual irradiation for forming apolycrystalline-Si film in a TFT device, preliminary irradiation isperformed in which the laser is irradiated on a pulse-by-pulse basisonto preliminary irradiation areas provided outside a target irradiationarea, on which the TFT device is to be formed. The preliminaryirradiation is performed while moving the irradiation position andchanging the irradiation intensity within a range over and below themelting intensity of the amorphous-Si film. The relationship between theirradiation intensity and the presence/absence of microcrystallizationis derived from the spectral measurement of a Raman light or scatteredlight for the preliminary irradiation areas, and the radiation intensityat which the microcrystallization starts is determined to be themicrocrystallization intensity.

According to the technique of the above patent publications, the actualirradiation is performed by irradiating the laser at the intensity lowerthan the microcrystallization intensity thus determined, which allowsthe microcrystallization of the amorphous-Si film to be prevented. Inthe technique of these documents, however, the spectral measurement of aRaman light or scattered light must be performed while the light sourcefor measurement and the light-receiving position for the reflected lightare moved to respective preliminary irradiation areas. This impedesimprovement in throughput of forming the polycrystalline-Si film.

SUMMARY OF THE INVENTION

It is therefore an exemplary object of the present invention to providelaser irradiation method and apparatus for crystallizing a semiconductorfilm, which is capable of providing a resultant film having a relativelylarge grain size and improving the throughput therein.

It is another exemplary object of the present invention to provide amethod and apparatus for detecting a microcrystallization intensity oflaser irradiated for crystallizing a semiconductor film.

It is a further exemplary object of the present invention to provide amethod for judging a grain size of a polycrystalline film.

The present invention provides, in a first aspect thereof, a methodincluding: scanning a semiconductor film on a substrate with laserhaving a specific lasing frequency at a plurality of irradiationintensifies to form a plurality of irradiation areas on thesemiconductor film each corresponding to one of the irradiationintensities; illuminating the plurality of irradiation areas in block toreceive light reflected from the irradiation areas in block; judging amicrocrystallization intensity based on the received reflected light;determining an irradiation intensity based on the microcrystallizationintensity; and scanning another semiconductor film with laser having thelasing frequency at the determined irradiation intensity to form acrystallized film.

The present invention provides, in a second aspect thereof, a methodincluding: scanning a semiconductor film on a substrate with laserhaving a specific lasing frequency at a plurality of irradiationintensifies to form a plurality of irradiation areas on thesemiconductor film each corresponding to one of the irradiationintensities; illuminating the plurality of irradiation areas in block toreceive light reflected from the irradiation areas in block; andmeasuring chromaticity of the received reflected light for each of theirradiation areas to detect a microcrystallization intensity based onthe measured chromaticity.

The present invention provides, in a third aspect thereof, a methodincluding: illuminating an area of a polycrystalline film to receivelight reflected from the area; dividing the area into a plurality ofdivided areas and measuring chromaticities of the received reflectedlight for the divided areas; and comparing the measured chromaticitiesagainst one another to judge a uniformity of chromaticity among themeasured chromaticities; and judging a uniformity of a grain size of thepolycrystalline film based on the judged uniformity.

The above and other objects, features and advantages of the is presentinvention will be more apparent from the following description,referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view showing the configuration of a laserirradiation apparatus used for a laser irradiation method according to afirst embodiment of the present invention;

FIG. 2 is a perspective view showing the positional relationship amongthe surface-light source unit, the substrate and the charge coupleddevice shown in FIG. 1;

FIG. 3 is a graph showing the relationship between the irradiationintensity and the surface roughness of the polycrystalline-Si film;

FIG. 4 is a top plan view showing the configuration of a substrate foruse in determining the microcrystallization intensity;

FIG. 5 is a flowchart showing the procedure of a laser irradiationprocess according to the first embodiment;

FIG. 6A is graph showing the relationship between the chromaticity x andthe irradiation intensity, and FIG. 6B is a graph showing therelationship between the chromatic difference Δx and the irradiationintensity;

FIG. 7 is a flowchart showing the procedure of a method of judging thegrain size uniformity according to a second embodiment of the presentinvention; and

FIG. 8 is a top plan view showing the substrate used in determining themicrocrystallization intensity used in the first embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, exemplary embodiments of the resent invention will be describedwith reference to accompanying drawings, wherein similar constituentelements are designated by similar reference numerals throughout thedrawings.

FIG. 1 is a top plan view showing the configuration of a laserirradiation apparatus, generally designated by numeral 10, for use in alaser irradiation method according to a first embodiment of the presentinvention. The laser irradiation apparatus 10 includes a laser source11, an optical system 12, a stage 13, a surface-light source unit 14 andan optical sensor configured by a charge coupled device 17. The laserirradiation apparatus 10 is used for melting and recrystallizing anamorphous-Si film formed on a surface of a substrate 16 to form apolycrystalline-Si film therefrom.

The laser source 11, which is an excimer laser device, generates a pulselaser having a predetermined lasing frequency toward the directiondenoted by “x”. The optical system 12 forms the laser 15 irradiated fromthe laser source 11 into an elongated rectangular shape, or linearshape, extending along the direction denoted by “y”. The substrate 16 isplaced on the stage 13, and the rectangular-shaped laser is irradiatedonto the surface of the substrate 16. The stage 13 is allowed to move inboth, the x- and y-directions in the state that the substrate 16 isplaced thereon.

FIG. 2 is a perspective view showing the positional relationship amongthe surface-light source unit 14, the substrate 16 placed on the instage 13 and the charge coupled device 17 shown in FIG. 1. Thesurface-light source unit 14 has a rectangular emitting surface 14 a.The surface-light source unit 14 is arranged so that the light emittingsurface 14 a makes an acute angle with respect to the surface of thesubstrate 16. A white flat light emitted in the direction perpendicularto the light emitting surface 14 a and having an approximately uniformintensity in the in-plane direction is irradiated from the lightemitting surface 14 a. The flat light emitted from the light emittingsurface 14 a illuminates a predetermined area, or illumination area 22,of the surface of the substrate 16. In this illumination, the flat lightirradiates respective portions of the illumination area 22 at a uniformintensity and a uniform incidence angle. The charge coupled device 17includes charge coupled elements capable of imaging three differentcolors including red, green and blue, and receives the reflected lightfrom the entire illumination area 22 in block for an image pick-upoperation.

FIG. 3 is a graph showing the relationship between the irradiationintensity of the laser and the degree of concavity and convexity, or thesurface roughness of the top surface of the polycrystalline-Si film,which represents the size of the crystal grain in the resultant film. Asshown in FIG. 3, along with the increase in the irradiation intensity,the surface roughness increases until the irradiation intensity reachesthe microcrystallization intensity. However, if the irradiationintensity exceeds the microcrystallization intensity, the surfaceroughness abruptly decreases. Meanwhile, the degree of the surfaceroughness significantly affects the chromaticity of the light reflectedfrom the surface of the polycrystalline-Si film. Especially, thechromaticity of the top surface of the polycrystalline-Si film changesdrastically with the microcrystallization intensity being the boundary.Based on this fact, the microcrystallization intensity is determined byusing the chromaticity so detected by the charge coupled device 17 inthe present embodiment.

In the laser irradiation process of the present embodiment, apreliminary irradiation is performed on a microcrystallization-intensityjudgment substrate 20 for the purpose of determining themicrocrystallization intensity, prior to the irradiation of a laser(actual irradiation) onto a target substrate on which thepolycrystalline-Si film is formed. FIG. 4 is a top plan view showing theconfiguration of the microcrystallization-intensity judgment substrate20. On the surface of the microcrystallization-intensity judgmentsubstrate 20, an amorphous-Si film is formed in advance using theprocess conditions similar to the process conditions in which thepolycrystalline-Si film is formed on the target substrate for theproduct. On the amorphous-Si film formed on themicrocrystallization-intensity judgment substrate 20, a plurality ofpreliminary irradiation areas 21 having an elongated rectangular shapeextending in the y-direction are arranged in the x-direction to form anarray. The illumination area 22 includes a plurality of thesepreliminary irradiation areas 21.

FIG. 5 is a flowchart showing the procedure of the laser irradiationprocess of the present embodiment. The substrate 20 is placed on thestage 13, and thereafter, the plurality of preliminary irradiation areas21 are irradiated with laser of different irradiation intensities withinthe range above and below the melting intensity of the amorphous-Si film(step S11). Subsequently, the surface-light source unit 14 irradiatesthe illumination area 22 of the substrate 20, and at the same time, thecharge coupled device 17 picks-up the image of the illumination area 22in block (step S12). Further, the chromaticity of each of thepreliminary irradiation areas 21 is measured from the image dataacquired by the image-pickup operation, and the measured chromaticity isevaluated for the value thereof (step S13). In the evaluation of thechromaticity, x-component chromaticity (chromaticity x) of the CIE(Commission Internationale d' Eclairage)-XYZ color system is used.

Subsequently, the relationship between the irradiation intensity and theamount of change, or chromaticity difference Δx effected in thechromaticity x is calculated with respect to change in the irradiationintensity, based on the relationship between the evaluated chromaticityx and the irradiation intensity (step S14). Further, the irradiationintensity where the change in the chromaticity x, i.e., the chromaticitydifference Δx assumes a maximum is detected and determined as themicrocrystallization intensity (step S15). In this step, a maximumchange in the chromaticity per unit change of said irradiation intensitycan be detected. Automated operation is performed using a computer toevaluate the chromaticity x, calculate the relationship between thechromaticity difference Δx and the irradiation intensity, and detect theirradiation intensity at which the chromaticity difference Δx assumes amaximum. The irradiation intensity to be used in the actual irradiationis determined based on the determined microcrystallization intensity(step S16).

FIG. 6A is a graph showing the relationship between the irradiationintensity and the chromaticity x measured for each of the preliminaryirradiation areas 21. FIG. 6B is a graph showing the relationshipobtained from FIG. 6A between the chromaticity difference Δx and theirradiation intensity. As understood from FIG. 6A, the chromaticity xincreases along with the increase in the irradiation intensity, showingan abrupt increase in the vicinity of the microcrystallization intensity(MCI). As understood from FIG. 5B, the chromaticity difference Δx has amaximum at the microcrystallization intensity. Thus, it is possible toaccurately determine the microcrystallization intensity by judging thatthe irradiation intensity at which the chromaticity difference Δx ismaximized is the microcrystallization intensity.

In the laser irradiation process of the present embodiment, theillumination area 22 is picked-up for image in block when theillumination area 22 is illuminated, whereby the light reflected fromthe preliminary irradiation areas 21 can be simultaneously received.This eliminates the necessity of moving the stage 13 or the chargecoupled device 17 for the determination of microcrystallizationintensity, thereby improving the throughput of the process. In addition,since the equipment necessary for moving the stage 13 or the chargecoupled device 17 is not required, a cost reduction is also achieved.The image-pickup of the illumination area 22 is performed by receivingthe light reflected from the entire preliminary irradiation areas 21 inblock. Thus, the number of pixels of the charge coupled device 17 can bereduced.

By determining that the irradiation intensity at which the chromaticitydifference Δx assumes a maximum is the microcrystallization intensity,the microcrystallization intensity can easily and accurately bedetermined. Since this allows adoption of an irradiation intensity whichis below the microcrystallization intensity in the actualrecrystallization for the product, it is possible to form apolycrystalline-Si film having a relatively large grain size withoutincurring the undesirable microcrystallization. Thus, a TFT devicehaving excellent characteristics such as a higher carrier mobility canbe obtained.

It is desirable for the irradiation intensity on the substrate to beuniform in the in-plane direction, in order for suppressing errors fromoccurring during measuring the chromaticity. For this purpose, it ispreferable that the area of the light emitting surface 14 a of thesurface-light source unit be larger than the total area of the pluralityof preliminary irradiation areas 21. In addition, it is preferable thatthe range of variation in the in-plane luminance of the light emittingsurface 14 a be 5% or less.

In the embodiment described above, the microcrystallization-intensityjudgment substrate 20 is provided separately from the target substratefor use in a product. It is also possible to use the same substrate andprovide therein the preliminary irradiation areas 21 and the area foractual irradiation separately. Further, the x-component of the CIE-XYZcolor system is used for evaluating the chromaticity. However, it isalso possible to use y-component, or both the x-component andy-component. Furthermore, in the determination of microcrystallizationintensity, it is also possible to evaluate the luminance in stead of thechromaticity.

FIG. 7 is a flowchart showing the procedure of a method for judging thegrain size uniformity in a laser irradiation process according to asecond embodiment of the present invention. In the method of the presentembodiment, judged is the uniformity of the grain size of thepolycrystalline-Si film formed by a laser irradiation. First, the laserirradiation apparatus shown in FIG. 1 is used, where the substrate for aproduct is placed on the stage 13, and the actual irradiation isperformed to form a polycrystalline-Si film of the TFT devices (stepS21). To form the polycrystalline-Si film, the irradiation intensity oflaser is set lower than the microcrystallization intensity.

Next, while allowing the surface-light source unit 14 to illuminate thetarget irradiation area which has been irradiated by laser, the chargecoupled device 17 picks-up the image of the target irradiation area inblock (step S22). A plurality of judgment regions are set within thetarget irradiation area, and the chromaticity of each of the judgmentregions is measured from the image data acquired by the image-pickupoperation for evaluation (step S23). In the process of evaluating thechromaticity, similarly to, e.g., the first embodiment, the x component(chromaticity x) in the CIE-XYZ color system is used. Subsequently, therange of variation in the chromaticity x (chromaticity variation) iscalculated from the measured chromaticity x in the respective judgmentregions, and this range of chromaticity variation is determined as therange of variation in the grain size (grain size uniformity) (step S24).In order to suppress possible errors in the measurement of thechromaticity, the light emitting surface 14 a of the surface-lightsource unit is set larger in area than the target irradiation area.

In the method of judging the grain size uniformity in the presentembodiment, the image of the target irradiation area is picked-up inblock while the area is illuminated, whereby the light reflected fromthe respective judgment regions is simultaneously received. Thiseliminates, similarly to the first embodiment, the necessity of movingthe stage 13 or the charge coupled device 17 in the determination ofgrain size uniformity, thereby improving the throughput of the process.In addition, the equipment necessary for moving the stage 13 or thecharge coupled device 17 is not required, thereby achieving a costreduction. The image-pickup of the target irradiation area can beperformed by receiving the light reflected from the entire judgmentregions in block. Thus, the number of pixels of the charge coupleddevice 17 can be reduced.

Since the grain size uniformity is acquired from the range of variationin the chromaticity, the in-plane grain size uniformity in the targetirradiation area can easily and accurately be judged. Based on the grainsize uniformity thus judged, the range of in-plane variation in theirradiation intensity and film-forming conditions of the laser arecorrected, thereby providing a polycrystalline-Si film having a smallerrange of in-plane variation in the grain size. Accordingly, TFT deviceshaving a smaller range of characteristic variation can be formed andproduct yield thereof is improved. Assuming that the process conditionsfor forming the film are uniform in the in-plane direction of the filmin the target irradiation area, the in-plane variation of the grain sizeobtained in the target irradiation area in the second embodimentprovides judgment of the range of in-plane variation for the laserirradiation intensity.

It is to be noted that although the preliminary irradiation and actualirradiation are performed on the same stage 13 in the embodimentsdescribed above, these irradiations can be performed on differentstages. Further, in the laser irradiation apparatus 10, for example, theactual irradiation can be repeatedly performed under the sameirradiation condition, whereby the relationship between the number ofirradiation times of laser and the chromaticity of the light reflectedfrom the target irradiation area are examined. This can determine thedegree of reduction in the irradiation intensity of the laser. Thedecrease and range of in-plane variation in the irradiation intensity oflaser occur by, e.g., a stain of the optical system 12.

A first example based on the laser irradiation process of the firstembodiment will now be described. FIG. 8 is a top plan view showing theconfiguration of the microcrystallization-intensity judgment substrateused in the first example. A glass substrate having a 370 mm×470 mm sizewas prepared. A SiO₂ film was formed having a thickness of 2000angstroms on the glass substrate, and an amorphous-Si film was formedhaving a thickness of 500 angstroms on the SiO₂ film, thereby achievingthe microcrystallization-intensity judgment substrate 20.

A plurality of preliminary irradiation areas 21 of themicrocrystallization-intensity judgment substrate 20 thus formed wereirradiated with pulse laser having different irradiation intensitieswithin the range above and below the melting intensity of theamorphous-Si film. The pulse laser was used to scan the plurality ofpreliminary irradiation areas 21 in the x-direction, whereby the entirepreliminary irradiation areas 21 were irradiated with the pulse laser.The lasing frequency of the pulse laser was 300 Hz, and the dimensionsof the irradiated laser were 350 mm (in y-direction)×0.4 mm (inx-direction). The scanning pitch was 0.04 mm so that the irradiatedlaser beams overlap one another at the overlapping rate of 90%.

Each preliminary irradiation area 21 has a 350 mm (in y-direction)×20 mmx-direction) size, with the space between adjacent preliminaryirradiation areas 21 was set at 1 mm. The irradiation intensity wasvaried within the range of 445 to 490 mJ/cm², with the irradiationintensity being changed at a uniform step of 5 mJ/cm² between adjacentpreliminary irradiation areas 21. Further, the illumination area 22 waspicked-up for image thereof by the charge coupled device 17 while beingirradiated with a while light. The charge coupled device 17 having400,000 pixels was used for the image pick-up operation.

In this example, five judgment regions 23 a to 23 e were provided ineach of the preliminary irradiation areas 21. The judgment regions 23 ato 23 e of each of the preliminary irradiation areas 21 were arranged ata regular interval in the y-direction and aligned in the x-directionwith the judgment regions 23 a to 23 e, respectively, in the otherpreliminary irradiation areas 21. In other words, the correspondingjudgment regions 23 a, for example, aligned in the x-direction configurea group of judgment regions. The diameter of the judgment regions 23 ato 23 e was set at 10 mm. The chromaticity x was numerically expressedfor each of the judgment regions 23 a to 23 e of the preliminaryirradiation areas 21 based on the image data obtained therefrom. Therelationship between the chromaticity difference Δx and the irradiationintensity in each group was calculated based on thenumerically-expressed chromaticity x.

As a result of the above process, both the relationship between thechromaticity x and the irradiation intensity and the relationshipbetween the chromaticity difference Δx and the irradiation intensity foreach group of the judgment regions 23 a to 23 e revealed a similartendency, such as shown in FIGS. 6A and 613. However, due to the rangeof in-plane variation in the irradiation intensity of the pulse laserbeams, for the case of groups of the judgment regions 23 a to 23 c, thechromaticity x increased abruptly and the chromaticity difference Δxassumed a maximum both at an irradiation intensity of 470 mJ/cm². On theother hand, for the case of groups of the judgment regions 23 d and 23e, the chromaticity x increased abruptly and the chromaticity differenceΔx assumed a maximum both at an irradiation intensity of 475 mJ/cm².Consequently, the local microcrystallization intensity in the judgmentregions 23 a to 23 c was determined to be 470 mJ/cm², whereas the localmicrocrystallization intensity in the judgment regions 23 d and 23 e wasdetermined to be 475 mJ/cm².

In the present embodiment, the local microcrystallization intensitiesobtained in the groups of judgment regions 23 a to 23 e were averaged,and the microcrystallization intensity was determined to be 472 mJ/cm².The average was derived from the calculation: 470×(⅗)+475×(⅖)=472. Inthis case, the range of in-plane variation in the irradiation intensitywas evaluated to be around 1.1% based on the calculation (475−470)/472.It is to be noted that it is also possible to select, for example, thelowest one of the above local microcrystallization intensities indetermination of the microcrystallization intensity.

In the above example, the microcrystallization intensity was determinedby averaging the local microcrystallization intensities measured for theplurality of groups of judgment regions 23 a to 23 e provided in thepreliminary irradiation areas 21. Consequently, possible errors due tothe range of in-plane variation in the irradiation intensity can bereduced in the determination of microcrystallization intensity. It ispreferable for the area of each judgment region 23 to occupy 1% or moreof the area of the corresponding preliminary irradiation area 21 inorder to determine the accurate microcrystallization intensity. Further,in the above embodiment, five judgment regions 23 were provided,whereas, if there are more judgment regions provided, themicrocrystallization intensity can be more accurately determined.

It is to be noted that if a single shot of pulse laser at theirradiation intensity higher than the microcrystallization intensity isirradiated on the surface of the amorphous-Si film, the regionirradiated with the pulse laser is microcrystallized. However, in therelatively narrow regions around the irradiated region of theamorphous-Si film, the temperature therein is higher than the meltingtemperature and lower than the temperature for the microcrystallizationintensity, causing the regions to be crystallized without themicrocrystallization. The same holds true for the case that the pulselaser is irradiated on the already microcrystallized regions before theirradiation, because the polycrystalline-Si film is melted andrecrystallized through the irradiation of the pulse laser. Thus, ifscanning irradiation is conducted at such an irradiation intensity overthe microcrystallization intensity, crystallized regions having a largegrain size periodically occur in the microcrystallized region.

Thus, a larger scanning pitch will provide a larger ratio of the area ofthe microcrystallized region relative to the area of the crystallizedregion, thereby allowing the change in the chromaticity at themicrocrystallization intensity to be significant. In particular, ascanning pitch of 0.01 nun or more will provide a significant change inthe chromaticity at the microcrystallization intensity, therebyfacilitating the determination of the microcrystallization intensity.

A second example based on the method of judging the grain sizeuniformity in the second embodiment will now be described. An isirradiation intensity of 450 mJ/cm², which is lower than themicrocrystallization intensity, was adopted for the actual irradiationthe second example, based on the microcrystallization intensity of 472mJ/cm² and the range of in-plane variation of 1.1% in the irradiationintensity, which were obtained in the first example. At this irradiationintensity, the actual irradiation was performed on the substrate for aproduct, to melt and recrystallize an amorphous-Si film, whereby apolycrystalline-Si film was formed. As in the case of the preliminaryirradiation, the lasing frequency of the pulse laser was set to 300 Hz,and the dimensions of the irradiated laser beam were 350 mm (iny-direction)×0.4 mm (in x-direction). The scanning pitch was set at 0.04mm.

While the surface-light source unit 14 irradiated the target irradiationarea, the charge coupled device 17 picked-up the image of the targetirradiation area in block. The chromaticity of the target irradiationarea was measured according to the thus picked-up image data. It wasconfirmed from the obtained chromaticity that the microcrystallizationhas not yet been caused and the grain size was relatively large.Further, a plurality of judgment regions were set in the targetirradiation area, and the range of chromaticity variation of thejudgment region was calculated, resulting in that there was a smallrange of variation. Thus, it was confirmed that the in of the crystalgrain was uniform in the in-plane direction of the film because of asmaller range of in-plane variation in the irradiation intensity of thepulse laser and the process conditions for forming the film.

Subsequently, TFT devices were fabricated. The average carrier mobilitywas 260 cm²/Vs, and the range of variation in the threshold of the TFTdevices was within 5%. Thus, it can be estimated that TFT devices havinga higher performance and a smaller range of characteristic variationwere achieved by the laser irradiation process of is the firstembodiment described above.

In the above-described examples, although the irradiation intensity inthe actual irradiation was lower than the microcrystallizationintensity, the present invention is not limited to use of an irradiationintensity lower than the microcrystallization intensity. For instance,Patent Publication JP-2003-332346A describes a method of controlling thelocations for forming crystal grains by irradiation of laser at anirradiation intensity above the microcrystallization intensity at apredetermined interval prior to formation of a polycrystalline-Si film.Although this process is different from a typical process for formingthe polycrystalline-Si film, an accurate microcrystallization intensityshould be determined also in this technique, in order to form reliablecrystal grains. In this technique, the laser irradiation processdescribed in the first embodiment and first example of the presentinvention may be preferably used.

In accordance with the first exemplary embodiment of the presentinvention, the illumination of the irradiation areas in block as well asthe receipt of the reflected light from the irradiation are in blockdoes not require moving device for moving the stage mounting thereon thesubstrate, light source for illumination and charge coupled device forreceiving the reflected light, to simplify the structure of the laserirradiating apparatus, and also improves the through during the judgmentof the microcrystallization intensity.

The present invention has been described based on its preferredembodiments as described above. The laser irradiation process and laserirradiation apparatus of the present invention are by no meansrestricted to the configurations of the above embodiments, and a laserirradiation process and laser irradiation apparatus which are modifiedor altered in varies different ways from the above embodiments will fallwithin the scope of the present invention.

1. A method comprising: scanning a semiconductor film on a substratewith laser having a specific lasing frequency at a plurality ofirradiation intensities to form a plurality of irradiation areas on thesemiconductor film each corresponding to one of said irradiationintensities; illuminating said plurality of irradiation areas in blockto receive light reflected from said irradiation areas in block; judginga microcrystallization intensity based on said received reflected light;determining an irradiation intensity based on said microcrystallizationintensity; and scanning another semiconductor film with laser havingsaid lasing frequency at said determined irradiation intensity to form acrystallized film, forming a semiconductor device on the crystallizedfilm, wherein said judging includes: determining a plurality of judgmentareas in each of said irradiation areas, each of said judgment areas ineach of said irradiation areas corresponding to one of said judgmentareas of the others of said irradiation areas to form a group of saidjudgment areas; comparing image data of corresponding said judgmentareas in each group against one another to detect a maximum change inthe chromaticity per unit change of said irradiation intensity in theeach group; selecting one of said maximum changes per unit change ofsaid irradiation intensity obtained in a plurality of said group; anddetermining said microcrystallization intensity based on said selectedmaximum change.
 2. The method according to claim 1, further comprisingjudging a range of variation in an irradiation intensity of said laserbased on a range of variation detected in said maximum changes per unitchange of said irradiation intensity.
 3. The method according to claim1, wherein said judgment areas each have an area equal to or above 1% ofan area of said each of said irradiation area.
 4. The method accordingto claim 1, wherein said illuminating uses a surface light source. 5.The method according to claim 1, wherein said another semiconductor filmis formed on said substrate.
 6. The method according to claim 1, whereinsaid another semiconductor film is formed on another substrate.
 7. Themethod according to claim 1, wherein said semiconductor film is anamorphous silicon film, and said crystallized film includespolycrystalline silicon.
 8. The method according to claim 1, whereinsaid plurality of irradiation intensities have a stepwise differencetherebetween.
 9. A method comprising: illuminating an area of apolycrystalline film with white light to receive light reflected fromsaid area; dividing said area into a plurality of divided areas andmeasuring chromaticities of said received reflected light for saiddivided areas; and comparing said measured chromaticities against oneanother to judge a uniformity of chromaticity among said measuredchromaticities; judging a uniformity of a grain size of saidpolycrystalline film based on said judged uniformity; and forming asemiconductor device when the uniformity of the grain size of thepolycrystalline film is equal to or lager than a predetermined value.